Patent literature 1: JP 2008-294299 A
For example, a press fit terminal has been known as a terminal (also referred to as a connection terminal) having spring property. It is supposed that a substrate, which is a connection target member, is connected with the press fit terminal. The press fit terminal has a greater width than a diameter of a through hole of the substrate. The press fit terminal is press fitted into the through hole of the substrate. And, by reaction force (referred to as spring reaction force) by elastic deformation of the terminal, the connection between the press fit terminal and the substrate is maintained. A wall surface of the through hole has a first connection portion including a plating film. A second connection portion of the press fit terminal contacts with the first connection portion under a pressurizing state according to the reaction force. That is, the second connection portion crimps the first connection portion. Thus, the first connection portion and the second connection portion are mechanically connected. Accordingly, the first connection portion and the second connection portion are electrically connected.
The connection between the press fit terminal and the substrate is required to have connection strength (a retention power) in order to endure external force such as a vehicle vibration and to maintain a contact state between the first connection portion and the second connection portion. However, the connection strength may decrease with variation of friction coefficient of a contact point between the first connection portion and the second connection portion. The press fit terminal may fall out according to the external force.
In order to increase the connection strength, the diameter of the through hole may be reduced, for example. Accordingly, the spring reaction force of the press fit terminal may increase. However, when the first connection portion and the second connection portion are connected mechanically, a damage given to the first connection portion and the second connection portion may enlarge, so that connection reliability may fall down. It may be difficult that sufficient connection strength is assured and damage at the time of mechanical connection is suppressed.
Patent literature 1 discloses an electronic apparatus that has a substrate including a first connection portion formed at a wall surface of a through hole and a plating film including copper as the first connection portion, and a press fit terminal including a second connection portion including copper or copper alloy. The second connection portion has a base material that includes copper or copper alloy as a constituent material, and a plating film formed as a constituent material of tin on the surface of the base material. In the electronic apparatus, a diffusion phenomenon of copper and tin is generated between the both plating films by heat of a core layer configuring the substrate under mechanical connection state. Thus, a diffusion joining is performed between the first connection portion and the second connection portion. Therefore, the electronic apparatus includes a joint portion formed with including a contact point of the first connection portion and the second connection portion.
The inventor of the present disclosure has found the following.
In the electronic apparatus of patent literature 1, the joint portion of the first connection portion in the substrate and the second connection portion in the press fit terminal has the following structure: a base material (copper) of the press fit terminal; a plating film (tin); a copper tin alloy; and a plating film (copper) of the substrate, in this order. The plating film (tin) formed on the surface of the base material and the alloy layer (the copper tin alloy layer) formed by the diffusion joining may have a shorter fatigue life than copper configuring the plating film of the first connection portion and the base material of the second connection portion. Therefore, when external force is repeatedly added to the joint portion, the fatigue life of the joint portion may shorten.